The continuous production of disposable absorbent articles, such as diapers, adult incontinence products, and feminine hygiene products generally involves periodic refills of raw materials delivered as a web from a wound roll, particularly for materials such as nonwovens and film stock. When each roll of raw material is nearly depleted, it is necessary to switch to a new roll without disrupting the continuous infeed of web to a converting system. This is typically accomplished by splicing the web of the new roll to the web of the nearly depleted roll using a mechanism well known in the art and commonly referred to as a splice box. An upstream process such as web unwinding and splicing as well as a downstream process such as rewind can both use an accumulator system to store an extra supply of web to be used during such processes.
Intermittent processes can use accumulators before and/or after a process operation to intermittently reduce web speed, in some cases to zero. The accumulator system can commonly take the form of either a linear system with translating rollers or a rotary system with rollers on a stationary arm and a pivotable arm. The translating rollers of a linear system are movable toward and away from one another along a generally linear path to decrease and increase the distance between rollers. Similarly, the rollers on the pivotable arm of a rotary system are movable toward and away from the rollers on the stationary arm along an arcuate path to decrease and increase the distance between rollers. In the case of some processes such as a splicing sequence, the raw material roll having a nearly depleted web supply will slow to a speed lower than full line speed or zero speed for the splicing function which can involve a process of affixing the web of a new roll to the web of the old, nearly depleted roll. The splice process can be via pressure sensitive adhesive, thermal bonding, ultrasonic bonding, pressure bonding or other processes known in the art and commercially available.
During either upstream or downstream processes, the accumulator system provides a continuous feed of the web to or from a converting system by changing the distance between rollers, or idlers, in the web path. The tension in the web and distances between rollers can change considerably during both upstream and downstream processes so such processes can be considered to be highly dynamic. These highly dynamic processes are known to cause out of plane web displacement which can result in web wrinkles, web foldovers, web neckdown, web break-outs, web mistrack, line stops, phase variation of cyclic product features, registration variation of intermittent product features, and defective products. A wrinkle on a roller is any out of plane displacement of the web from the surface of a roller. A foldover on a rollover is defined here as any cross-section of material on a roller where three or more layers of material are present on one cross-section of material on the surface of a roller. A foldover is a type of wrinkle. Due to the wide range of process conditions that can be encountered, these problems have not been adequately addressed in a manner avoiding such adverse consequences. In particular, existing methods to mitigate wrinkle and foldover formation often cause unintended adverse effects, such as web mistrack and high drag forces. Also, it has not been considered possible to utilize lower basis weight webs, thinner webs, and non-homogenous web cross sections due to wrinkling problems presented by highly dynamic accumulation processes, or due to adverse effects of the countermeasures intended to mitigate wrinkling.
If the foregoing adverse consequences could be avoided over the wide range of process conditions encountered in the continuous production of disposable absorbent articles and in the production of raw materials for such disposable absorbent articles, such as diapers, adult incontinence products, and feminine hygiene as well as baby wipes and other such products, it would be possible to significantly reduce manufacturing costs by making it possible to use less expensive materials such as lower basis weight webs, thinner webs, and non-homogenous web cross sections while at the same time reducing equipment cost, increasing line reliability and increasing operating speeds.